1 . Field of the Invention
The disclosed embodiments of the present invention relate to a flash memory, and more particularly, to a method for managing data stored in a flash memory and related memory apparatus and controller.
2 . Description of the Prior Art
A flash memory can be used to store data through electrical erase and write/program, and is widely applied in the field of memory cards, solid-state drives, portable multi-media players, etc. Because the flash memory is a non-volatile memory, there is no need for extra power to maintain what is stored in the flash memory. In addition, the flash memory provides high speed data access and excellent vibration resistance, which explains its popularity.
The flash memories can be classified into two categories: NOR flash memories and NAND flash memories. For the later, the erase time and program time is shorter, and the die size of each memory cell is smaller. Thus, compared with the NOR flash memory, the NAND flash memory permits higher storage density and lower cost per bit. Generally speaking, the flash memory consists of memory cell arrays, wherein each memory cell is implemented using a floating-gate transistor in practice, and the threshold voltage of the memory cell is configured by properly controlling charge number at a floating gate of the floating-gate transistor to thereby store a single-bit data or a multi-bit data. Therefore, when one or more predetermined control gate voltages are imposed at the control gate of the floating-gate transistor, a conduction status of the floating-gate transistor will indicate one or more binary digits stored in the floating-gate transistor.
However, due to certain reasons, the original charge number of the flash memory may be affected/disturbed. For instance, the disturbance may come from retention disturbance, and a number of charges stored in the flash memory may changes due to high temperature . Hence, threshold voltage distribution of memory cells of the flash memory may change by the effect of retention time and/or temperature, and the data read from the memory cells may be erroneous since the threshold voltage distribution may be different from the original threshold voltage.